java反射基础API

Java反射代码 得到某类的所有字段 getxxx()与getDeclaredxxx()区别

 

* getFields()与getDeclaredFields()区别:

getFields()只能访问类中声明为公有的字段,私有的字段它无法访问.getDeclaredFields()能访问类中所有的字段,与public,private,protect无关

* getMethods()与getDeclaredMethods()区别:

getMethods()只能访问类中声明为公有的方法,私有的方法它无法访问,能访问从其它类继承来的公有方法.getDeclaredFields()能访问类中所有的字段,与public,private,protect无关,不能访问从其它类继承来的方法

* getConstructors()与getDeclaredConstructors()区别:

getConstructors()只能访问类中声明为public的构造函数.getDeclaredConstructors()能访问类中所有的构造函数,与public,private,protect无关

 

test：

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

import sun.reflect.generics.tree.ClassTypeSignature;

public class DumpMethords {
	private String info;
	private String info1;
	private int age;

	public DumpMethords(){}
	public DumpMethords(String info){ System.out.println(info);}
	public void test1(){
		
	}
	public void test2(){
		
	}
	public void test3(){
	
	}
	public static void main(String[] args) throws ClassNotFoundException, SecurityException, NoSuchMethodException, IllegalArgumentException, IllegalAccessException, InvocationTargetException, InstantiationException {
		String str = "abc";
		//四种获得classObject的方法
		//Class classesType = str.getClass();
		//Class classesType = Class.forName("java.lang.String");
		//Class classesType = String.class;
		//Class classesType = Integer.TYPE;
		Class classesType = (new DumpMethords()).getClass();
		Method methods[]  = classesType.getDeclaredMethods();
		for(Method m : methods)
			System.out.println(m.toString());
		Constructor<DumpMethords>[] cs = classesType.getConstructors();
		System.out.println("----------------------");
		for(Constructor<DumpMethords> c:cs){
			System.out.println(c.toString());
		}
		System.out.println("----------------------");
		Constructor<DumpMethords> c = classesType.getConstructor(new Class[]{String.class});
		System.out.println(c.toString());
		System.out.println("----------------------");
		Field[] fields = classesType.getDeclaredFields();
		for(Field f:fields){
			System.out.println(f.toString());
		}
		System.out.println("----------------------");
		Field[] field = classesType.getFields();
		for(Field f:field){
			System.out.println(f.toString());
		}
		
		System.out.println("--------获得特定方法-----------");
		Method sAge = classesType.getMethod("setAge",new Class[]{Integer.TYPE});
		Method gAge = classesType.getMethod("getAge",null);
		Object[] args1 = new Object[]{new Integer(23)};
		Object o = classesType.newInstance();
		sAge.invoke(o, args1);
		System.out.println(gAge.invoke(o, null));
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	public String getInfo() {
		return info;
	}
	public void setInfo(String info) {
		this.info = info;
	}
	public String getInfo1() {
		return info1;
	}
	public void setInfo1(String info1) {
		this.info1 = info1;
	}
}

 object is not an instance of declaring class 反射异常的解决方法：

第一种：反射执行的方法 setAge() 、getAge() 改成静态的

第二种：在执行方法前先实例化类。m.invoke(classesType,null)改为m.invoke(classesType.newInstance(),null)或者m.invoke(new DumpMethords(),null)

 

 

reference：

http://blog.csdn.net/yeson6/archive/2011/01/14/6138963.aspx

http://hi.baidu.com/xfpsh/blog/item/9375da425757071b9313c69b.html